The aims of this proposal are to provide an understanding in molecular terms of the interactions between sensitized lymphocytes and macrophages which lead to the various manifestations of cell-mediated immune reactions. The focus is on the biochemical mechanisms by which macrophages can be activated to carry out various effector functions. The approach to these goals is through the use of genetic manipulation of continuous cloned macrophage-like cell lines, and the selection of variants in various macrophage specific differentiated functions. The functions of individual Fc receptors for immunoglobulins of various subclasses, as determined by monoclonal antibodies, are being studied by means of mutants, specifically IgG2a and IgG2b Fc receptor mutants. The former mutant is of particular interest since its expression is regulated by cyclic nucleotides. A second major interest is the role of neutral proteases, particularly plasminogen activator, in the regulation of macrophage function, and protease mutants are being sought. Finally, in order to study the mechanisms by which macrophages kill intracellular parasites, we have isolated a clone, J774.16, which under appropriate stimuli produces a respiratory burst, with production of O2- and H2O2 comparable to BCG-activated primary macrophages. From this, we have selected a mutant incapable of showing any oxidative metabolism, providing a useful model for chronic granulomatous disease, and an extraordinary tool for understanding the enzymes involved in producing the bactericidal radicals and the role of oxygen radicals in killing a variety of intracellular parasites.